It is a known technique to measure a voltage value and an impedance value of a fuel cell and determine an abnormality on the basis of these values. For example, a shortage or lack of hydrogen gas in an anode electrode (hydrogen starvation), a shortage or lack of oxygen in a cathode electrode (oxygen starvation), the drying of an electrolyte membrane (dry-out) and the like are considered abnormalities of the fuel cell. It is necessary to properly determine the hydrogen starvation, as it is a particularly important problem out of these events considered as abnormalities of the fuel cell.
A hydrogen concentration measurement method for estimating that a hydrogen concentration of an anode is relatively low (i.e. a hydrogen starvation state) when an arc of an internal impedance of a fuel cell drawn in a so-called Cole-Cole plot diagram is relatively large is proposed in WO 2010/128555.